1. Field of the Invention
The present invention relates to an electromagnetic valve actuating system for opening and closing intake and exhaust valves of an engine under electromagnetic forces generated by an electromagnet.
2. Description of the Related Art
Some conventional actuating systems for opening and closing intake and exhaust valves include a single camshaft which has cams to operate the intake and exhaust valves, the camshaft being disposed above or laterally. The camshaft is connected to the crankshaft of the engine by a belt or the like, so that the camshaft can rotate synchronously with the rotation of the engine.
In these conventional systems, the valves are pressed by cam surfaces of the camshaft through a link mechanism such as rocker arms or push rods. The intake and exhaust valves are normally closed by springs, and can be opened when their stem ends are pressed by the cam surfaces.
In alternative conventional systems, an intake camshaft having cams for acting on intake valves and an exhaust camshaft having cams for acting on exhaust valves are disposed above an engine. The intake and exhaust valves are opened when the stem ends of the intake valves are directly pushed by the cam surfaces of the intake camshaft and the stem ends of the exhaust valves are directly pushed by the cam surfaces of the exhaust camshaft.
However, the above conventional actuating systems for opening and closing intake and exhaust valves have several disadvantages. First, the conventional systems include camshafts and link mechanisms which must be added to the engine, and which necessarily renders the engine large in size.
Secondly, since the camshafts and the link mechanisms are driven by the output shaft of the engine, the engine output power is partly consumed due to the frictional resistance produced when the camshafts and the link mechanisms are driven by the engine. As a result, the effective engine output power is reduced.
Finally, the timing with which the intake and exhaust valves are opened and closed cannot be altered during operation of the engine. Instead, the valve opening and closing timing is preset such that the engine operates with high efficiency only when it rotates at a predetermined speed. Therefore, the engine output power and efficiency are lower when the engine rotates at a speed different from the predetermined speed.
To solve the above problems, there have been proposed valve actuating systems for opening and closing intake and exhaust valves under electromagnetic forces from electromagnets, rather than with camshafts, as disclosed in Japanese Laid-Open Patent Publications Nos. 58-183805 and 61-76713.
However, the coils of the electromagnets disclosed in the above publications must be supplied with large electric energy in order to generate electromagnetic forces large enough to actuate the intake and exhaust valves. As a result, the coils radiate a large amount of heat. As the electromagnets are associated with a cooling unit having a considerable cooling capacity, the problem of the large engine size still remains unsolved.